A. Field of the Invention
This invention relates to the art of rotary impact wrenches of a type in which a rotating member is periodically reciprocated into and out of rotary impacting relation with an anvil portion of a torque output shaft.
B. Description of the Prior Art
The evolution of powered impact wrenches includes one example in U.S. Pat. No. 3,428,137 which issued Feb. 18, 1969 for an "Impact Wrench". Some of the aspects of the prior art are the lack of a good pilot arrangement to position the lugs of the dog hammer to the anvil. The use of a spline connection between parts of the anvil does not ensure proper alignment of the hammer dogs and the anvil and causes loading on the bearing supports. Some past problems noted were loosening of the anvil bushing and cam shaft breakage. Also the prior art spline connection of the anvil parts affords little support for the anvil. Extra machining of parts was required by some of the prior art designs which added to the expense of the tool and the time required to make it. When light weight materials were tried in prior art devices the inertia of the moving parts was transmitted to the operator holding the tool.